1. Field of the Invention
Embodiments of the invention relate to a single-chamber cardiac stimulator, in particular an implantable cardiac pacemaker or an implantable cardioverter/defibrillator, with a right-ventricular electrode line. At least one right-ventricular sensing electrode and one right-ventricular stimulation electrode are attached to this electrode line; in the individual case, these electrodes may also be formed by a single electrode pole, which then serves as both the stimulation electrode and as the sensing electrode.
2. Description of the Related Art
A single-chamber cardiac stimulator is understood here to refer to a cardiac stimulator, which in the usual nomenclature is capable of recording an intracardiac electrocardiogram via a corresponding sensing electrode in only one chamber of the heart and delivering stimulation pulses only to this ventricle via a corresponding stimulation electrode. The stimulation electrode and the sensing electrode may be different from one another or may be formed by the same electrode pole. A single-chamber cardiac stimulator should also be understood here to refer to a cardiac stimulator, which may essentially also be connected to sensing electrodes in multiple chambers of the heart and thus may serve as a multi-chamber cardiac stimulator, but during operation the latter is connected only to an electrode line for sensing and/or for stimulation in a cardiac chamber.
One advantage of such a single-chamber cardiac stimulator is its fundamentally simple design combined with the fact that only a single electrode line need be implanted in a patient's heart.
There are various algorithms for discriminating between ventricular tachycardias (VT) and supraventricular tachycardias (SVT). None of the algorithms that require information about the atrial rhythm can be used for single-chamber ICDs. For these single-chamber ICDs, the sudden onset of tachycardia and the RR interval stability are established criteria for VT/SVT discrimination. In addition, these criteria are supplemented by an evaluation of the QRS complex morphology. However, these morphology-based algorithms have only limited suitability because the QRS morphology, derived in just one ECG lead in a VT, can be represented as unchanged in comparison with sinus rhythm. In these cases, a VT would be wrongly classified as an SVT and therefore would not be treated.
FIG. 6 illustrates such an example. This diagram shows the ECG before and during a ventricular tachycardia. In the channel labeled as FF, the far-field ECG lead between the ventricular shock electrode and the housing of the ICD is shown. The two marked QRS complexes show the QRS morphology in sinus rhythm and during a ventricular tachycardia. It can be seen clearly here that the morphologies are the same and thus do not constitute a basis for discrimination.